Association between gingivitis, tooth loss and cardiovascular risk: Insights from a 10-year nationwide cohort study of 3.7 million Koreans

Background While studies have suggested an association between periodontal disease and an increased risk of cardiovascular disease, the strength of this association and its specific links to various types of cardiovascular disease have not been thoroughly investigated. This study aimed to examine how gingivitis and tooth loss affect cardiovascular diseases, probing their individual impacts. Methods A retrospective cohort study was conducted, encompassing 3,779,490 individuals with no history of cardiovascular disease, utilizing data from the National Health Examination and the Korean National Health Insurance database from 2006 to 2019. Cox proportional hazards models were applied to estimate the association between tooth loss, gingivitis, and cardiovascular disease. Results Following a median follow-up of 10.38 years, 17,942 new cardiovascular disease cases were identified, comprising 10,224 cases of angina pectoris, 6,182 cases of acute myocardial infarction, and 9,536 cases of stroke. It was observed that the risk of stroke was significantly higher in the tooth loss group compared to the control group (adjusted hazard ratio [aHR]: 1.09, 95% confidence interval [CI]: 1.04–1.15). In the group with gingivitis and tooth loss, the risk of stroke and cardiovascular disease was significantly higher than in the control group (aHR: 1.12, 95% CI: 1.04–1.20; aHR: 1.08, 95% CI: 1.03–1.14). The gingivitis group exhibited a higher risk associated with stroke (aHR: 1.05, 95% CI: 1.01–1.10) among individuals aged 50 and above. However, statistically significant associations between periodontal disease and angina pectoris were not observed, nor between periodontal disease and acute myocardial infarction except among those aged above 50. Furthermore, the association between periodontal disease and cardiovascular disease was found to be stronger among individuals over the age of 50, males, those with obesity, and smokers compared to the control group. Conclusions Our results emphasize the association of tooth loss and gingivitis with cardiovascular disease, specifically stroke, underlining the critical need for preventive oral healthcare. Tailored interventions are necessary to reduce the heightened risk of cardiovascular disease events, especially stroke, among older, obese individuals and smokers.


Introduction
Periodontal diseases (PD), including dental caries, periodontitis, and tooth loss, affect more than 44.5% of the global population according to the 2019 Global Burden of Disease [1].Approximately 42% of adults in the United States suffered from periodontitis and 11% suffered from tooth loss from 2009 to 2014 [2].In South Korea, PD is ranked as the most frequent outpatient disease, with an estimated 17.4 million cases in 2021 [3].PD is an inflammatory disease that progresses to gingivitis, periodontitis, and tooth loss, and the progression of this disease is caused by the activity of periodontal pathogens such as Porphyromonas gingivalis (P.gingivalis), Aggregatibacter actinomycetemcomitans (A.a), Tannerella forsythia (T.Forsythia) and Treponema denticola (T.denticola) [4].Although most cases of PD are mild and preventable [5], they can be associated with chronic diseases such as cardiovascular disease (CVD) [6,7].
In recent decade, studies on link between PD and CVD have examined worldwide.Previous case-control studies [8,9], prospective cohort studies [6,[10][11][12], and retrospective cohort studies [13][14][15][16][17] reported that PD is associated with a high risk of CVD and Coronary Heart Disease (CHD).Studies have reported that oral bacteria such as P. gingivalis act on the immune system to coexist with the microbiome and cause inflammatory diseases [18][19][20][21], and this chronic immune response can affect the whole body.Another explanation for the observed association could be that the two disease entities share common risk factors such as smoking, diabetes, age, low socioeconomic status, physical inactivity, dyslipidemias, and alcohol consumption [22].
CVD continues to be the primary contributor to global disease burden.Its prevalence continues to increase over several decades in nearly all countries except those in the high-income category [23,24].In South Korea, CVD had been the second common cause of death in 2021, reporting 61.5 mortality (per 100,000 population) based on data on causes of death from the National Statistical Office.
Although growing evidence suggests a link between PD and CVD, but the strength of the association and the specific types of CVD affected with adjustment by multiple confounders are still unclear.Previous studies investigating PD and CVD risk had several limitations, such as lack of information on multiple confounding factors [8,9,11,12,15], use of self-reported diagnosis of PD [6,9,13], insufficient number of cases [8,9,13,15,17], and population of specific age groups [6,9,13,17].In contrast to previous studies that investigated the impact of periodontitis [6,9,12,14,15] and tooth loss [6,11,25] as primary explanatory variables on CVD, this study defined gingivitis and tooth loss as the oral health variables and explored the effects of both conditions.Unlike periodontitis, which represents the progression stages of PD, defining gingivitis expands the scope of investigation, enabling the capture of the entire spectrum of periodontal pathology, including early-stage symptoms.Therefore, gingivitis may play a more sensitive role in assessing oral health-related risk factors associated with CVD.Moreover, studies analyzing the risk of CVD through tooth loss are limited by their restriction to specific genders [6] and lack comprehensive investigation of CVD [11,25].
As Korean government examines a mandatory health examination including oral screening for all individuals above 20 years old, standardized data of all examinees, totaling 3.7 million, were collected from dentists, consisting of two PD-gingivitis and tooth loss.By combining the National Health Insurance claim data of these examinees, the association between PD and total CVD, angina pectoris (AP), acute myocardial infarction (AMI), and stroke (ST) risks was investigated on overall and sub groups.This study aimed to investigate the impact of gingivitis and tooth loss on CVD, as well as their specific effects on each CVD.Identifying individuals at higher risk through early onset and progression of PD could facilitate early intervention and promote early prevention strategies to mitigate CVD risks.

Study design and participants
This study was designed a population-based, retrospective cohort study using National Health Insurance Service (NHIS) database from 2006 to 2019 in Korea.The NHIS serves as the predominant insurance provider in Korea covering almost all citizens and playing a role in ensuring the accessibility of healthcare services to the population.Individuals enrolled in the insurance system are eligible to receive standardized medical examinations for health screening every two years.These examinations involve measurements of height, weight, and blood pressure (BP), fasting blood sugar (FBS), and also include oral examination.
In South Korea, since 1980, the National Health Examination Program for all citizens has been implemented under the National Health Screening Act, aimed at early detection and treatment of diseases.As a result, uniquely worldwide, a national health screening system spanning the entire lifespan, divided into infants, students, and adults, has been introduced, with the oral examination system also established as part of it, aimed at early detection and treatment of oral diseases [26].The examination institution refers to designated dental clinics where at least one dentist who has completed the oral examination institution education program designated by the Minister of Health and Welfare, along with at least one nurse or dental hygienist, works, as well as hospitals or public health centers with dental departments established, or general examination institutions that employ dentists solely for the purpose of oral examinations.The procedure involves completing a personal medical history questionnaire, undergoing an oral examination by a dentist, and then receiving individualized examination results notification and counseling.
The retrospective cohort consisted of 3,779,490 adults aged 20 years or older who examined oral screening between January 1, 2009 and December 31, 2009.Based on the entire Korean population who received oral examinations in 2009, claims data including medical records from the NHIS and health examination data from 2006 to 2019 were integrated.The index date was the date of the first oral examination in 2009, followed up for 10 years.During the year 2009, individuals who underwent oral examinations two or more times within a year were identified, and consequently, 5,076 of duplicated data beyond the initial instance were excluded Moreover, participants who died within 1 year (n = 6,591) and those diagnosed with CVD as a primary or secondary disease according to ICD-10 codes within 1 year after followup (n = 141,268) were excluded.The medical utilization history for the previous three years, retrievable through the cohort constructed based on the registration date of the study, was set as the washout period for medical history assessment.During the washout period of the study subjects from 2006 to 2008, patients (n = 44,512) with CVD diagnosis codes identified at least once as primary or secondary diseases were considered CVD patients and thus excluded from the study subjects.Finally, 107,680 participants with missing values in the independent variables, tooth loss, and gingivitis items in the oral examination data, were excluded (Figs 1 and  2).This study was approved by the Institutional Review Board at Korea University (KUIRB-2021-0131-02).The methods were performed in accordance with relevant regulations.Informed consent was waived because the NHIS database contains publicly available anonymized data.

Assessment of PD and CVD
Periodontal disease refers to a series of inflammatory conditions affecting the tissues surrounding and supporting the teeth, including the gums, periodontal ligament, and alveolar bone.This disease typically begins with gingivitis, an inflammation of the gums caused by plaque accumulation, and can progress to more severe forms such as periodontitis.Periodontitis involves inflammation extending deep into the supporting structures of the teeth, resulting in bone loss and potential tooth loss [2,4,5].In the ICD-10, periodontal disease is classified under code K05.Specifically, it is categorized into gingivitis (K05.0),periodontal disease (K05.1),aggressive periodontitis (K05.2),chronic periodontitis (K05.3),periodontosis (K05.4),other periodontal diseases (K05.5), and unspecified periodontal disease (K05.6).
Since most dental treatments are included in the non-coverage category, there is a problem that most oral diseases using health insurance claim data are omitted as treatment codes, so we used oral examination data which is conducted by dentists once every two years to detect oral diseases such as gingivitis and tooth loss at an early stage for adults in Korea.During the examination, gingivitis and tooth loss were diagnosed using probe and teethridge by a dentist.Adults who underwent a nationwide oral examination from January to December 2009 were determined to have each periodontal disease according to the criteria below.All independent variables were binary.Additionally, the results were derived by processing the group into a group with both gingivitis and tooth loss and a group with neither.
Gingivitis.Gingivitis was determined by visual inspection of gingival bleeding or gingival enlargement in the following cases: (1) Cases where the gums show slight redness and bleeding upon insertion of the probe; (2) Cases where the gums show overall severe inflammation, color change, loss of stippling can be observed, and spontaneous bleeding occurs.If there were no external signs of inflammation or bleeding, it was determined that there was no gingivitis.
Tooth loss.Tooth loss was determined in the following cases: (1) When one or more teeth are lost due to dental caries; (2) When restoration of function is necessary through tooth restoration.If there was an implant or processed tooth that did not require additional treatment, it was not judged as tooth loss.

Statistical analysis
The student t-test for continuous variables and Chi-square test for categorical variables were performed to compare the general characteristics of participants with PD and without disease.Continuous variables were presented as means ± standard deviation (STD) and categorical variables were presented as number (%).Multivariable Cox proportional hazard regression model was performed to calculate adjusted hazard ratios (aHR) and 95% confidence intervals (CI) of PD and CVD under different periodontal status.The model was adjusted for ten covariates (age, sex, income level, BMI, hypertension, diabetes, dyslipidemia, smoking history, alcohol intake and physical activity).All statistical analyses were performed using SAS Enterprise Guide version 7.15 (SAS Institute, Inc., Cary, NC, USA).Statistical significance was set at a two-sided p-value < 0.05.

General characteristics
At the baseline, of 3,779,490 participants, 984,192 had gingivitis (26.0%), 683,630 had tooth loss (18.1%), and 245,675 had both (6.5%).Participants with tooth loss at baseline were older (62.6±13.1),male, lowest income level (16.3%) and had higher BP, BMI, FBS and TC than participant without tooth loss.Additionally, participants with tooth loss more likely to be current smokers (33.4%), had higher frequency of alcohol (≧3 per a week, 16.2%) than participant without tooth loss.The gingivitis group comparing to non-gingivitis showed similar trends to the tooth loss group.Baseline characteristics of the participants are summarized in Table 1.

Risks (aHR) of CVD in patients with gingivitis and tooth loss
After a median of 10.38 years, 17,942 new CVD cases, 10,224 AP cases, 6,182 AMI cases, and 9,536 ST cases were identified.The risk of ST was significantly higher in the tooth loss group than the control group after adjustment (aHR: 1.09, 95% CI: 1.04-1.15).In the group with both gingivitis and tooth loss (G&T), the risk of ST and CVD were higher than the control group significantly (aHR: 1.12, 95% CI: 1.04-1.20;aHR: 1.08, 95% CI: 1.03-1.14)(Table 2).

Subgroup analyses of risks (aHR) of CVD in patients with gingivitis and tooth loss
The subgroup analyses for comorbidity and smoking status are presented in Tables 4 and 5.In the case of obese participants, all CVD risks tended to be higher compared to normal participants.In particular, among obese participants, those with tooth loss had a higher risk of ST (aHR: 1.12, 95% CI: 1.03-1.21),and those with G&T had a higher risk of CVD (aHR: 1.09, 95% CI: 1.01-1.19).As a result of stratification according to dyslipidemia, no clear trend was found, but the risk of AMI was 16% higher in the gingivitis group with dyslipidemia (aHR: 1.16, 95% CI: 1.01-1.32).Even if the cholesterol level was normal, the risk of ST was still significantly high when they had tooth loss or G&T (aHR: 1.09, 95% CI: 1.03-1.15;aHR: 1.11, 95% CI: 1.03-1.20),and the risk of CVD was significantly high when they had G&T (aHR: 1.08, 95% CI: 1.02-1.14).

Discussion
In this large retrospective cohort study of Korea, a clear positive association between PD and the risk of ST and CVD was documented.Particularly, these associations were stronger in participants with male, those who were older (�50 than <50), obesity, and smokers.After stratified by dyslipidemia, there was no consistent trend.
Most previous studies reported that PD increases the risk of CVD, and studies reported the magnitude of the risk to be between 1.10 and 1.30, which was similar to the 1.08 times in our study [6,8,25,31,32].In some cases, studies showed values more than 2.0 times higher, but they appear to have been overestimated because many confounding factors were not controlled [33].In particular, among the detailed diseases, there were many reports of ST.PD is thought to clearly increase the risk of ST, and the magnitude of the risk was similar, ranging from 1.12 in this study to 1.10-1.30 in other studies [8,11,17,25,[32][33][34][35].There was also a study that showed a high impact with a risk of more than 3 times, and this appears to be because the long observation period of more than 30 years and severe PD such as periodontal bone loss were independent variables [36].Among the specific diseases, there are inconsistent results regarding the association between PD and AMI, and there is a lack of evidence for the association.Howell et al. [13] showed a weak association of 1.12, Noguchi et al. [37] showed a high risk of 2.26, and Lee et al. [38] showed a low risk of 0.95.All these studies were not statistically significant.On the other hand, Yu et al. [39] reported a high risk of 1.72 significantly, but PD was self-measured, and the study was conducted on a single gender (female) without adjusting for alcohol drinking, etc.Moreover, Ryde ´n at al. [40] reported a high risk of 1.28.However, as the sample size was insufficient as a case-control study, it seems that well-designed large-scale data studies should be accumulated.In this study, most confounding factors were controlled to confirm the causal relationship between PD and specific CVD, and as a result of 10-year follow-up, a non- significant risk of 1.01-1.07was observed, confirming that the association with PD and AMI was weak.Regarding AP, there are few studies on the association, and similar to this study, the results were not statistically significant [38].
The impact of PD on CVD, especially ST, presented in this study is likely to result from chronic inflammation caused by gingivitis and periodontitis.Chronic PD causes immune dysregulation and systemic inflammation, and the role of oral pathogens such as P. gingivalis has been suggested [21,[41][42][43].Specifically, pathogenic microorganisms in periodontitis release inflammatory cytokines, chemokines, proteolytic enzymes, and reactive oxygen species through interactions with tissues and cells, causing local and irreversible degeneration of periodontal structures.Infectious agents and inflammatory mediators can spread throughout the body, causing inflammatory conditions and promoting the development of systemic diseases.In addition, interleukin (IL) 1β, IL-6, or tumor necrosis factor (TNF) are reported to affect cardiovascular disease by circulating throughout the body and causing responses in other tissues [43].Additionally, it has recently been suggested that the atherosclerotic process that causes ST is an immune-metabolic response of blood vessels to various harmful factors [44,45].
Meanwhile, as a result of sub-group analysis to control residual confounding effects, the effect was evident in older, male [46,47], and smoking in particular appears to be a major factor increasing the effect [6,10,11,25,48].PD and CVD are closely related as they share risk factors such as smoking, diabetes, obesity, lack of physical activity, and stress, so additional research is needed to uncover this connection [6,9,11].In addition to age, an additional point to note is that although the effect is mostly large and shows a significant trend in the elderly, a few studies have shown a high risk of ST even in young participants [35].In this study, only in the case of ST, the risk in participants under 50 years of age was 1.71 and significant.Managing PD will be very important to prevent ST in young people.
While numerous studies have explored the link between PD and CVD, analyses of specific CVD with each sub groups on all age adults are rare.One of the strengths of our study was that the large-scale data consisted of nearly 3.7 million participants who have undergone mandatory National oral examination for one year, so it is representative with no recall bias and little selection bias.This big data defines PD through clinical examinations by dentists and clinically defines CVD using health insurance claim data, so it has higher clinical reliability than selfmeasurement and surveys.In addition, we attempted to derive accurate results by correcting ten confounding variables, including comorbidities.Despite these strengths, this study has several limitations.Variables for PD were recorded in a binary format, so differences in disease severity could not be analyzed.Additionally, as tooth loss is a time-dependent variable, the cumulative effect due to chewing discomfort and deterioration in quality of life will change.Therefore, it is suggested that follow-up studies examine the effect of tooth loss according to the duration.Moreover, since the explanation of the mechanism for the association between the two diseases identified in this study could not be measured, further experimental study on mechanism is needed.Lastly, this study did not reflect the severity of CVD.

Conclusions
Our results highlight an association between tooth loss, gingivitis, and the occurrence of CVD, specifically ST, emphasizing the critical need for preventive oral healthcare interventions.Additionally, our findings indicate the necessity for tailored interventions aimed at reducing the heightened risk of CVD events, particularly ST, among older, obese individuals and smokers.